1. Field of the Invention
The present invention relates to a portable, assemblable-disassemblable staircase assembled by continuously connecting an upper and lower flights stair unit for use in a house or a store.
2. Description of the Prior Art
Various types of portable, assemblable-disassemblable staircases are well known in the art. One of such staircases is disclosed in Japan Patent Application Serial No. 62-13459, which comprises a cylindrical upward joint and a cylindrical downward joint which are vertically installed at a rear end and a front end of a horizontal base plate, a stair unit connected to upper and lower flights by uniting the upward joint and the downward joint, a fixing plate welded horizontally within the downward joint and provided vertically with a transparent hole in its center, a movable case connected to an end of the upward joint and inserted rotatably into the downward joint to move up and down together with the upward joint, a covering plate welded horizontally to the movable case and provided with a nut welded to its center, a bolt spirally inserted into the nut from the transparent hole so as to fix the fixing plates of the upper and lower stair units and the covering plate, and a tread fixed to the upper surface of each horizontal base plate.
The other of such staircase is disclosed, in Japan Patent Application Serial No. 62-13460 publication 62-13459, which comprises a stair unit wherein a cylindrical upward joint and a cylindrical downward joint are vertically installed at a rear end and a front end of a horizontal base plate, a fixing bolt is vertically installed in the upper central part of the upward joint, a horizontal seating plate is fixed within the downward joint, and the upward and downward joints of upper and lower stair units which are rotatably inserted/united are fixed by holding the horizontal seating plate between upper and lower nuts which are spirally united with the fixing bolt.
However, such staircases as described hereinabove require the fixing plate, the movable case, and the covering plate in addition to the cylindrical upward joint, the cylindrical downward joint, and the connection bolt as parts necessary to connect the upper stair unit and the lower stair unit.
Therefore, they require a large number of basic elements and weighs. Also, it takes a long time and they require more efforts because they entail welding of the fixing plate to the downward joint, screwing of the movable case and the upward joint, screwing of the covering plate to the movable case, and welding of the nut to the covering plate.
Furthermore, they require an assistant worker for holding the stair unit at a position where it is to be installed while an angle at which the upper and lower stair units are to be placed is adjusted by turning it and fixed by the bolt because the cylindrical upward and downward joints must be inserted and secured rotatably. Fitting of the stair units is also troublesome and labor cost is thereby made to go up.
Furthermore, as the bolts and the nuts are arranged on the longitudinal central line of the upward and downward joints, the upward and downward joints can be made rotatable when one of the bolts is loosened by an unknown cause, and fixed condition of the upper and lower stair units may be distorted and the stair case may thereby tremble dangerously.
Also, the fixing bolt is placed on the longitudinal central line of the upward joint. Therefore, when the bolt is loosened by an unaccountable cause, the upward and downward joints can be made rotatable and the fixed condition of upper and lower stair units may be distorted and the staircase may thereby tremble.